Entrance-exit atmospheric isolation device

ABSTRACT

An atmospheric isolation device for separation of two atmospheres of a continuous semiconductor processing apparatus which includes a gas entry tube, a plurality of first gas restricting means leading to a first atmosphere, a plurality of second gas restricting means leading to a second atmosphere, and adjacent to each gas restricting means an expansion chamber for increasing back pressure and for destroying lift produced by the Bernouilli effect of the gas passing through the restricting means.

United States Patent Garnache et al.

[ Feb. 29, 1.972

[54] ENTRANCE-EXIT ATMOSPHERIC ISOLATION DEVICE [72] Inventors: RichardR. Garnache, South Burlington;

Donald M. Kenny, Shelburne, both of Vt.

[73] Assignee:

International Business Machines Corporation, Armonk, NY.

[22] Filed: July 30, 1970 [211 App]. No.: 59,496

- 521 ..277/72 SR, 1 18/49 51] ..B65d 53/00 58 Field of Search..118/48-49.5, 50,

[56] References Cited umrso STATES PATENTS 2,580,976 1/1952 Toulmin',Jr. ..1 18/495 3,473,510 10/1969 3,531,319 9/1970 Martorana Sheng et al...118/49.5 ...1 18/48 X FOREIGN PATENTS OR APPLICATIONS 766,459 1/1957Great Britain ..118/49 Primary ExaminerMorris Kaplan Attorney-Hanifinand Jancin and Howard J. Walter Y ABSTRACT An atmospheric isolationdevice for separation of two atmospheres of a continuous semiconductorprocessing apparatus which includes a gas entryvtube, a plurality offirst gas restricting means leading to a first atmosphere, a pluralityof second gas restricting means leading to a second atmosphere, andadjacent to each gas restricting means an expansion chamber forincreasing back pressure and for destroying lift produced bytheBemouilli effect of the gas passing through the restricting means.

9 Claims, 3 Drawing Figures Pa tented Feb. 29, 1912 3,545,545

INIVENTORS mm GARNACHE Fl (5. 3 DONA KENNEY BY WM AGENT 1 ENTRANCE-EXITATMOSPHERIC ISOLATION DEVICE BACKGROUND OF THE INVENTION 1. Field of theInvention This invention relates to isolation devices used to separatetwo different atmospheres in continuous semiconductor processingapparatus, and more particularly to the structure of an entry-exit sealfor continuous vapor deposition apparatus of the types disclosed incopending applications: Ser. No. 345 filed on Jan. 2, 1970, and entitledMethod and Apparatus for Diffusion Limited Mass Transport" or Ser. No.825,827 filed May 19, 1969, and entitled Continuous Systems forFabricating Semiconductor Substrates to Contain a Diffused ConductivityType Determining Impurity Therein, both assigned to the assignee of theinstant invention.

2. Description of the Prior Art Atmospheric isolation devices of theprior art are found to consist of three basic types: (1) restrictedaperture types, (2) positive pressure types and (3) negative pressuretypes. These devices find application in various processing apparatuswhere it is desirable to prevent gaseous phase material, or othercontaminants, from passing through an opening through which workpiecesmust pass. These devices are most appropriately used between ambientatmosphere and reaction vessel atmosphere, such as found in vapordeposition or sputtering apparatus. v

The restricted aperture prior art device consists of a relatively long,low ceilinged, or restricted, passage which utilizes gas viscosity incombination with a gas pressure head developed over an extented distanceto maintain positive controlled flow in a direction either toward oraway from a particular part of the apparatus. These devices have theirprimary application where a relatively large pressure differentialexists between the two atmospheres, for example, ambient atmosphere anda pressure vessel.

The positive pressure devices utilize a multiple stream concept whereina single external gas stream, usually an inert gas, is divided such thatpart of the gas flows into the ambient and part flows into theprocessing vessel, thereby preventing the mixing of gases of the twoatmospheres to be isolated. This type device has its primary applicationin apparatus where the mixing of two atmospheres on both sides of theseal is not permissible, for example, where the process gas is explosivein air.

Negative pressure devices are constructed similarly to the positivepressure types but the gas flow is reversed. Gases are drawn from boththe process vessel and the atmosphere to prevent leaking of the processgases into the atmosphere.

The above-described prior art devices, although effective in certainapplications, prove to be undesirable in the semiconductor processingapparatus disclosed in the above-referenced applications. The prior artdevices require, depending on the type used, either high-gas flow ratesor high-back pressure. Furthermore, when reasonable stream velocitiesneeded to provide a proper margin of safety are used, sufiicient lift isdeveloped by the Bernouilli effect to cause semiconductor substrates tobe lifted bodily from their carriers, thereby causing irreparable damageto the substrates.

SUMMARY OF THE INVENTION It is therefore an object of this invention toprevent damage to semiconductor wafers while passing from one atmosphereto another in a semiconductor processing system.

It is another object to provide an improved structure for a gaseousphase isolation device having improved efficiency without increasingcosts for materials.

It is a further object of this invention to provide an effective gaseousphase isolation device which uses relatively low-back pressures moreefficiently than prior art devices.

The invention herein disclosed is constructed to realize theaforementioned objects, goals and advantages, and comprises in itspreferred form a positive pressure isolation device having a gas inletmeans and two atmospheric communicating passages. The passages areformed by a series of alternating restricted apertures and expansionchambers. The restricted apertures provide means to increase backpressure and limit gas flow rates, while the expansion chambers providerelief from the Bernouilli effect caused by the restrictions and alsoproduce a drop in enthalpy, or internal energy, of the gas stream byallowing controlled expansion, thereby allowing higher pressures to beused than possible with the low ceiling, or extended restrictedaperture, type devices.

The foregoing and other objects, features and advantages of theinvention will be apparent from the more particular description of apreferred embodiment of the invention as illustrated in the accompanyingdrawing.

BRIEF DESCRIPTION OF THE DRAWING DETAILED DESCRIPTION OF THE INVENTIONAlthough the structure of the instant invention may be utilized aseither an entry, exit or intermediate isolation device, only theapplication as an exit seal need be discussed in detail, as thestructure and operation of the device is independent of its location inthe processing apparatus.

Referring now to FIG. 1 there is shown the isolation device 10 of theinstant invention mounted on the exit end of the process apparatus 12 ofthe aforementioned copending application, Ser. No. 345, the descriptionand operation of which is herein expressly incorporated by reference.The isolation device is mounted on plate 14 which may be bolted, orotherwise attached, to the process apparatus. Mounted in a recess oncarriers 16 shown leaving the isolation device 10, are semiconductorsubstrates 18. In operation, carriers 16 are continuously passed throughthe apparatus. Inlet gas tube 20 mounted on the top of isolation deviceIt) is provided to supply inert gas, for example argon, or othersuitable gas, to effectuate operation of the device. Tube 20, normallyis connected to a metered source of inert gas, not shown. It shouldbeunderstood that the operation of the device is independent of theparticular gas used and that any gas compatible with the two atmospheresto be isolated may be used.

Referring to FIG. 2, gas is delivered in a downward direction, asindicated by arrow 21, through tube 20 into chamber 22 from which itexits through gas restricting means, apertures 24 and 26. The restrictedapertures are formed partially by the upper surface of carrier 16 andsubstrates l8 and partially by projections 28 of a top plate 30.Projections 28 may be formed by transverse grooves milled into top plate30 or may be separately constructed and mounted into position. The shapeof the restricted apertures is a gap of uniform width formed by thesubstantially parallel spaced relation between the upper surfaces ofcarriers 16 and substrates R8 and the lower edges or surface ofprojections 28.

Located adjacent to apertures 24 and 26 are expansion chambers 32 intowhich the gas then passes. Thereafter, there are provided a series ofalternating restricted apertures 24 and I6 and expansion chambers 32,the particular number and size of which is optional depending upon thedesired design characteristics of the isolation device as will bediscussed below.

Carriers l6, normally consisting of machined high purity graphite,supporting semiconductor substrates 18 are continuously passed throughthe apparatus, for example, from left to a right.

FIG. 3 shows a sectional view of the isolation device and more clearlyillustrates the shape of restricted apertures 26 and expansion chambers32. The carriers 16 are shown supported by bottom plate 34 and guidedthrough recess 35. Both bottom plate 34 and top plate 30 may beconstructed of stainless steel or other suitable material compatiblewith the atmospheres found in the process apparatus.

ln summary, it will be seen that there is provided a gas inlet tube 20and a plurality of first gas restricting means, apertures 24, leading tothe first atmosphere, or the processapparatus, and a series of secondgas restricting means, apertures 26, leading to the second or ambient,atmosphere, and adjacent to each gas restricting aperture is anexpansion chamber 32.

The particular number, size and location of the various elements of theisolation device are best determined depending on' the particular inertgas used, as well as the processing system requirements.

A typical example of an application of theinstant invention would be ina vapor deposition process such as. silicon deposition. In such a systemit is desirable to utilize a certain net gas flow rate into the processapparatus to assure proper operation and safety of the system. Forexample, 1 liter per minute through a 4 inch wide restriction would betypical. Utilizing this flow rate and providing a typical gasrestricting aperture size of 0.010 inch, the linear gas flow rate at theprocess side of the device would be about 5 centimeters per second,depending upon the width of carrier 16. I

In order to determine the appropriate thickness of each projection 28and thereby set the effective lift produced by the flowing gas,Bernouillis equation must be used.

In its simplest form Bernouillis equation may be written as:

When applied to the lifting of a substrate from its carrier, P and Vrefer to the underside of the substrate where the velocity is zero and Pand V refer to the top side of the substrate. It is obvious that at anystreaming velocity the pressure gradient will be such as to provide alifting force. Applying a minimum safe streaming velocity of 5centimeters per second with, for example, argon gas having a density (p)of 1.78 grams per liter and utilizing a substrate area of 2.57 l" squaremeters the lift obtained is approximately 5.7 grams. Since the typicalwafer weighs approximately 3 grams it must lift off the carrier. Thesolution as described herein is to provide a thickness for projection 28which will reduce the effective lift area of reduced pressure to preventthe lifting of substrates. With a weight of 3 grams and a lift factor of5.7 grams over the area of the wafer, it is obvious that a reduction insurface area of 50 percent is required to prevent lifting of the wafer.This can be accomplished by a combination of equal width expansionchambers and gas restricting apertures. The spacing between thesubstrate and the aperture will determine the pressure required toproduce the 5 centimeter per second streaming velocity through one setof gas restricting apertures and expansion chambers. The number ofapertures and expansion chambers will determine the overall systempressure. Apparatus constructed in accordance with the above descriptionhaving expansion chambers produces four times the back pressure of asmooth restricted aperture at the same streaming velocity. For example,a back pressure of approximately 4 ounces may be expected to provide aflow rate of 1 liter per minute through the device into the processapparatus, having an internal pressure of 0.1 ounce.

A similar determination may be made for the second, or ambient,atmosphere side of the isolation device. Typically a flow rate of twicethat flowing into the process apparatus is desirable for the ambientside of the device, that is, a series of five sets of expansion chambersand apertures.

It should be understood that the structure of the above described deviceis not limited to positive pressure operation and may in someapplications be utilized with a negative presdescribed with reference toa preferred embodiment thereof,

it will be understood b those skilled in the art that various changes inthe form an details may be made therein without departing from thespirit and scope of the invention.

What is claimed is:

1. Apparatus for providing isolation between a first atmosphere and asecond atmosphere comprising:

a gas inlet means;

a plurality of first gas restricting means for allowing a con trolledquantity of gas to pass from said gas inlet means to said firstatmosphere; atmosphere;

a plurality of second gas restricting means for allowing a controlledquantity of gas to pass from said gas inlet means to said secondatmosphere; atmosphere;

at least one gas expansion chamber located adjacent to each one of saidfirst and second gas restricting means for interrupting the Bemouillieffect created by said gas restricting means and for further providing areduction in enthalpy by allowing controlled expansion of gas toincrease back pressure.

2. Apparatus in accordance with claim 1 wherein said gas restrictingmeans are of equal size.

3. Apparatus in accordance with claim 1 wherein said gas restrictingmeans are substantially in the shape of an aperture formed by twosubstantially parallel spaced surfaces.

4. Apparatus in accordance with claim 3 wherein said gas restrictingmeans are formed partially by projections having a substantially flatsurface and partially by substantially flat workpieces.

5. Apparatus in accordance with claim 3 wherein the width of saidprojections and said expansion chambers are substantially equal.

6. Apparatus for providing isolation between ambient atmosphere and acontinuous semiconductor processing apparatus atmosphere comprising:

gas inlet means;

a plurality of first gas restricting means for allowing a controlledquantity of gas to pass from said gas inlet means to said room-ambientatmosphere;

a plurality of second gas restricting means for allowing a controlledquantity of gas to pass from said gas inlet means to said continuoussemiconductor processing apparatus atmosphere, said first and second gasrestricting means being defined partially by semiconductor substratesurfaces and a substrate carrier and partially by a carrier conformingmember mounted in parallel spaced relation to the surface of thecarrier, said restricting means further comprising an effective liftarea less than necessary to lift substrates from their carriers; and

at least one gas expansion chamber located adjacent to each of saidrestricting means for disrupting the Bemouilli effect produced by aflowing gas stream passing through said restricting means and forcreating a reduction in enthalpy by means of controlled expansion of gasto increase back pressure.

7. Apparatus in accordance with claim 6 wherein said carrier conformingmember comprises a substantially flat surface.

8. Apparatus in accordance with claim 6 wherein said first and secondgas restricting means are of equal size.

9. Apparatus in accordance with claim 6 wherein the total width of onegas restricting means and one gas expansion chamber together equals lessthan the width of one semicon ductor substrate.

( 223? UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3, 645, 545 Dated February 29, 1972 lnv tofl Richard R. Garnache andDonald M. Kenney It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

Column 4, Line 15 after "atmosphere;" delete atmosphere; Column 4, Line18, after "atmosphere;" delete atmosphere; and substitute therefor andSigned and sealed this 6th day of February 1973.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTISCHALK Attesting Officer Commissionerof Patents

1. Apparatus for providing isolation between a first atmosphere and asecond atmosphere comprising: a gas inlet means; a plurality of firstgas restricting means for allowing a controlled quantity of gas to passfrom said gas inlet means to said first atmosphere; atmosphere; aplurality of second gas restricting means for allowing a controlledquantity of gas to pass from said gas inlet means to said secondatmosphere; atmosphere; at least one gas expansion chamber locatedadjacent to each one of said first and second gas restricting means forinterrupting the Bernouilli effect created by said gas restricting meansand for further providing a reduction in enthalpy by allowing controlledexpansion of gas to increase back pressure.
 2. Apparatus in accordancewith claim 1 wherein said gas restricting means are of equal size. 3.Apparatus in accordance with claim 1 wherein said gas restricting meansare substantially in the shape of an aperture formed by twosubstantially parallel spaced surfaces.
 4. Apparatus in accordance withclaim 3 wherein said gas restricting means are formed partially byprojections having a substantially flat surface and partially bysubstantially flat workpieces.
 5. Apparatus in accordance with claim 3wherein the width of said projections and said expansion chambers aresubstantially equal.
 6. Apparatus for providing isolation betweenambient atmosphere and a continuous semiconductor processing apparatusatmosphere comprising: gas inlet means; a plurality of first gasrestricting means for allowing a controlled quantity of gas to pass fromsaid gas inlet means to said room-ambient atmosphere; a plurality ofsecond gas restricting means for allowing a controlled quantity of gasto pass from said gas inlet means to said continuous semiconductorprocessing apparatus atmosphere, said first and second gas restrictingmeans being defined partially by semiconductor substrate surfaces and asubstrate carrier and partially by a carrier conforming member mountedin parallel spaced relation to the surface of the carrier, saidrestricting means further comprising an effective lift area less thannecessary to lift substrates from their carriers; and at least one gasexpansion chamber located adjacent to each of said restricting means fordisrupting the Bernouilli effect produced by a flowing gas streampassing through said restricting means and for creating a reduction inenthalpy by means of controlled expansion of gas to increase backpressure.
 7. Apparatus in accordance with claim 6 wherein said carrierconforming member comprises a substantially flat surface.
 8. Apparatusin accordance with claim 6 wherein said first and second gas restrictingmeans are of equal size.
 9. Apparatus in accordance with claim 6 whereinthe total width of one gas restricting means and one gas expansionchamber together equals less than the width of one semiconductorsubstrate.